1. Field of the Invention
The present invention relates to a method of controlling a chemical solution applying apparatus, a chemical solution applying apparatus, and a method of manufacturing a semiconductor device, and in particular, to a method of controlling a chemical solution applying apparatus that applies a chemical solution such as resist to a substrate such as a semiconductor wafer, the method being used for a process of manufacturing, for example, a semiconductor device, a flat display panel (FPD), or a micro-electronics micro-system (MEMS).
2. Description of the Related Art
In recent years, the manufacture of semiconductor devices has needed to adjust to low-volume high-mix production. In the low-volume batch production, the amount of chemical solutions used varies significantly among the types of semiconductor devices, however, the process does not require so much amount of chemical solutions. Thus, chemical solutions staying in piping may be degraded and fail to exhibit desired performance.
Under these circumstances, Jpn. Pat. Appln. KOKAI Publication No. 2003-266006 discloses a technique for a chemical solution applying apparatus having a control section that functions to discharge resist (i.e., chemical solution) that has stayed in piping for a predetermined time period, on the basis of the characteristics of resist. However, if the quality preservation period of the chemical solution is short and only a small amount of the chemical solution is infrequently used during manufacture, a large amount of chemical solution is uselessly discharged every time the predetermined time elapses. The amount of chemical solution uselessly discharged may reach several hundred cubic centimeters. Further, a pump for a dispenser system is normally optimized for small-amount dispensations. Consequently, discharging a large amount of chemical solution requires a very long time, that is, several tens of minutes. The discharge process must be completed before a new chemical solution can be dispensed and applied to substrates. Thus, a large amount of chemical solution discharged disadvantageously results in the need for a long time for a process of applying the chemical solution to substrates.
To solve this problem, it is possible to increase the frequency or amount of dummy chemical solution dispensation (i.e., chemical dispensation for discharge, that is, chemical solution dispensation carried out while no lots (semiconductor substrates) are processed) that is set so as to prevent the chemical solution from being solidified at the tip of a nozzle; this prevents a degraded chemical solution from being dispensed to substrates. However, this method frequently carries out dummy dispensations even during the frequent processing of lots. As a result, the method disadvantageously fails to reduce the amount of useless chemical solutions.